One objective of this study is to investigate the biochemistry of the fusion that occurs between the plasma membranes of the sperm and egg during fertilization of the sea urchin. Because of evidence in other systems implicating lysophospholipids in membrane fusion processes, the primary emphasis will be on the role of phospholipases in the fusion, although the possibility that other enzymes are involved will be investigated. Purified phospholipid specifically labeled in the fatty acyl chains, will be synthesized and employed for assay of the phospholipase. Synthetic substrates for other catabolic enzymes such as proteases, phosphatases, and glycosidases are commercially available. Of particular interest is the function of the sperm acrosome in membrane fusion. The distribution of catabolic enzymes in the acrosome and the acrosome membrane will be studied. Also to be investigated will be the possibility that a latent phospholipase is activated upon initiation of the fertilization process. This study will be done under conditions of polyspermic fertilization, in order to maximize the level of phospholipase and/or lysophosholipids that may be produced during the fusion of the anterior membrane of the acrosomal process of the sperm with the plasma membrane of the egg. The second objective is to characterize any generalized changes that occur in components of the plasma membrane of the zygote following fertilization. A comparative study of possible alterations in the synthesis of proteins, glycoproteins, and phospho- and glycolipids will be made on the plasma membranes of unfertilized and fertilized eggs.